Sensors and detection systems for detecting physical quantities such as an electric field and a magnetic field are disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication (JP-A) No. Sho 59-166873) and Patent Document 2 (Japanese Unexamined Patent Application Publication (JP-A) No. Hei 2-28574).
FIG. 1 is a sectional view showing the structure of a conventional high-spatial-resolution electric field sensor using an optical technique and FIG. 2 is a diagram showing an example of a detection system using the electric field sensor of FIG. 1.
Referring to FIG. 1, an electric field sensor 905 is bonded to the tip of an optical fiber 901 through an adhesive layer 906. The electric field sensor 905 comprises a fine electrooptical crystal 907 serving as an electric field detection element and a dielectric multilayer reflective layer 908 formed on a bottom surface of the electrooptical crystal 907 for reflecting light.
Referring to FIG. 2, the detection system comprises a continuous laser light source 900, fiber amplifiers 902 and 911, a polarization controller 903, an optical circulator 904, the electric field sensor 905 provided over a circuit board 909 being an object to be measured, an analyzer 910, a photodetector 912, optical fibers 901 connecting them to each other, and a spectrum analyzer 913.
The electric field detection principle of this detection system will be briefly described hereinbelow. Light emitted from the continuous laser light source 900 is amplified by the fiber amplifier 902 and subjected to control of its polarization plane by the polarization controller 903 and then is incident on the electric field sensor 905 through the optical circulator 904. The incident light on the electric field sensor 905 is reflected by the dielectric multilayer reflective layer 908 formed on the bottom surface of the electrooptical crystal 907 and then is again returned into the optical fiber 901. Since the electrooptical crystal 907 changes its refractive index depending on an electric field generated from the circuit board 909, the polarization state of the laser light propagating in the crystal changes while being subjected to modulation according to the intensity of the external electric field. The modulated light again passes through the optical circulator 904, then is converted into intensity-modulated light by the analyzer 910 and amplified by the fiber amplifier 911, and then is converted into an electrical signal by the photodetector 912.
The electrical signal is detected by the spectrum analyzer 913 and a peak that occurs at that time is determined to be a signal caused by the external electric field. On the principle of this detection system, the signal intensity differs depending on the intensity of the external electric field and, therefore, the electric field distribution is obtained by changing the position of the electric field sensor 905 over the circuit board 909.
Incidentally, by replacing the electrooptical crystal 907 in FIG. 1 with a magnetooptical crystal, the system of FIG. 2 becomes a magnetic field detection system having high spatial resolution. The magnetic field detection principle in this case can be explained by replacing “electric field” with “magnetic field” in the foregoing explanation of the electric field detection principle.
As described above, the conventional electric field detection system or magnetic field detection system having high spatial resolution is characterized by having the structure in which the microfabricated electrooptical crystal or magnetooptical crystal is bonded to the tip of the optical fiber 901.
An application region and spatial resolution of an electric field detection system or a magnetic field detection system are limited by the size of an electrooptical crystal or a magnetooptical crystal and, as the size decreases, the system can be applied to a smaller region and has a higher spatial resolution. The spatial resolution is determined based on the volume of sensor light propagating in the crystal and, as the volume of the sensor light decreases, the spatial resolution increases. For example, to describe a conventional magnetic field sensor in which a magnetooptical crystal is bonded to the tip of an optical fiber, the magnetic field sensor having a 10 μm-class spatial resolution is realized using the crystal having a plane size of 270 μm×270 μm and a thickness of 11 μm.
However, with such a structure, it is difficult to realize a further reduction in size and a further increase in spatial resolution of a sensor due to the limitation of the crystal microfabrication technique and, thus, it is not possible to provide a sensor applicable to a very small region of an LSI chip/package.
Further, in the case of the conventional type sensor, since the crystal is bonded to the tip of the optical fiber as described above, loss of light is caused by the adhesive layer and this loss causes a reduction in sensitivity of the sensor and thus makes it difficult to detect a very small electric field or magnetic field generated from an LSI chip or the like.
It is an object of this invention to realize a sensor having high sensitivity and high spatial resolution while being smaller in size than the conventional electric field/magnetic field sensor, thereby providing the sensor applicable to a very small region of an LSI chip/package.